SINCE the beginning of the sixteenth century, when the clouds of the middle ages were broken by the first sun-glimpse of reawakening reason, the average longevity of the North Caucasian nations has increased nearly seven years. In Northern Europe and North America the progress in the practice, if not the science, of healthy living has, indeed, kept fairly step with the general advance of civilization; the worst heresies against the health-laws of Nature have become errors of the past. Unventilated dwellings have become unpopular. Phlebotomy has gone out of fashion. We have ceased to fuddle our children with beer-soup. Hygienic reform has everywhere modified our habits of life.

Yet the principle of that reform has strangely failed to be recognized. For one invalid who can steer a straight course to the harbor of health, a thousand weather the breakers in a random, empiric way, like untrained sailors, failing to comprehend the purpose of the beacon, though using its light to avoid the nearest cliffs. Nay, if the source of that light were indiscreetly revealed, it would frighten hundreds back into utter darkness, to scan the firmament for a glimpse of its vanished loadstars, rather than trust their safety to an earthly guide. For, with the progress of a practical regeneration, a theoretical adherence to the traditions of the past still goes hand in hand. Not all civilized Buddhists have renounced the Dalai Lama; and many of our progress-loving contemporaries would be rather alarmed at the discovery that the principle of our social, medical, and educational reforms during the last two hundred years has been a restored trust in the competence of our natural instincts. So foreign was that rule of conduct to the moral standards of the middle ages that its importance was recognized only in its apparent exceptions, the supposed "evil propensities of our unregenerate nature," such as poison-habits, sloth, and sexual excesses. The real significance of such aberrations-would reveal the difference between natural appetites and abnormal (artificially acquired) appetencies, and teach us the necessity of applying the tests of that distinction to all persuasive instincts, and occasionally to otherwise unexplained aversions.

But even within those limits a critical study of our protective intuitions would surprisingly show in how many respects the hygienic reforms of the last two hundred years could have been anticipated by the simple teachings of our senses. For the wards of instinct a temperance sermon would be as superfluous as a lecture on the folly of drinking boiling petroleum, for to the palate of a normal living being—human or animal—alcohol is not only unattractive, but violently repulsive, and the baneful passion to which that repugnance can be forced to yield is so clearly abnormal that only the infatuation of the natural depravity dogma could ever mistake it for an innate appetite. In defense of the respiratory organs. Nature fights almost to the last. The blinded dupe of the night-air superstition would hardly assert that he finds the hot miasma of his unventilated bedroom more pleasant than fresh air. He thinks it safer, in spite—or perhaps because—of its repulsiveness. "Mistrust all pleasant things" was the watchword of the mediaeval cosmogony. Long before Jahn and Pestalozzi demonstrated the hygienic importance of gymnastics, children embraced every opportunity for outdoor exercise with a zeal which only persistent restraint could abate. Sexual aberrations are a consequence, oftener than a cause, of disordered health. Instinct has always opposed the abuse of drugs, the delusions of asceticism, the suicidal follies of fashion. Instinct has never ceased to urge the reforms which our times have at last reached by such circuitous roads, and the study of its pleadings and protests might shorten those roads for the leaders of future generations.

On the other hand, it must be admitted that perverted appetites can become as irresistible as the most urgent natural instincts. Nor can it be denied that in some exceptional cases Nature fails to advise us of perils which her warning could easily avert, though we should remember that her standards of expediency are not always our own, and that, as a rule, instinct asserts itself at the fittest times, and with an urgency proportionate to the importance of its mission.

The exceptions, thus far only partly explained, may be summed up under the three following heads: 1. Perverted Instincts.—The physiology of certain abnormal propensities is as obscure as the origin of sin. There is no doubt that the innate aversion to any poison known to modern chemistry can, by persistent disregard, be turned into a morbid appetency, vehement and persistent in proportion to the virulence of the poison. The most plausible hypothesis suggested in explanation of that fact seems to be the conjecture that, in adapting itself to the exigencies of abnormal circumstances, the constitution of the organism has to undergo certain modifications, considerable in extreme cases, and correspondingly less easy to undo. For every "second nature" is, probably, a compromise with the persistency of untoward conditions. Iron-workers become less sensitive, and at last rather partial, to the fervid temperature of their workshops. Butchers, like the North American Indians, and other carnivora, are apt to contract a disposition which enables them to pursue their sanguinary vocation with callousness, or something akin to satisfaction. .Slaves become sneaks, i. e., amateur flunkeys. The love of light, too often punished with autos-da-fé, becomes a love of dusk, if not of darkness; the Arian skeptic subsides into a resigned Capuchin—Nature forbears to maintain a hopeless struggle. For similar reasons, perhaps, she yields to the persistent infatuation of the self-poisoners, called topers and opium eaters. Further resistance would imply chronic sea-sickness, and, under the circumstances, an abnormal fondness for strong drink may appear a lesser evil. Yet the characteristics of such propensities distinguish them clearly from a natural instinct; they have to be artificially acquired, their importunity knows no limits, and their free indulgence is always followed by a depressing reaction. Thus, even in yielding. Nature remains true to her preordained laws. No one can hope to evade their self-avenging rigor, though the mode of retribution may take the unexpected form of chaining the miscreant to his idol

2. Abnormal Perils.—The dangers incident to our artificial modes of life seem now and then to deceive the foresight of instinct in a way typified in the non-repulsiveness of certain mineral poisons. Nature has taken ample precautions to secure her creatures against the poison perils of the upper world—hemlock, foxglove, and belladonna—but failed to provide safeguards against such subterranean evils as arsenic, or the social dangers yet slumbering in the womb of Time. Providence, however, may have foreseen that perils evoked by the potent hand of Science could be avoided in the same way; though the struggle for existence may, in the course of time, evolve supplementary instincts. Those fittest to survive, methinks, already begin to evince an intuitive aversion to the sugar-coated poisons that have reduced our average longevity to less than forty years. The world is getting prudent by natural selection. The children of the twentieth century will not be apt to overrate the nutritive value of fusel-oil.

3. Parasitic Disorders.—The healing instincts of Nature, which teach the surfeited brute to abstain from food, somehow fail to take cognizance of the disorders caused by the agency of microscopic parasites, entozoa, etc. It has been suggested that the development of such organisms is as foreign to the autonomy of the human system as the growth of the mistletoe is to that of the oak, and thus escapes the jurisdiction of its self-regulating laws. But a still more suggestive circumstance is the fact that disorders of the class named reveal their origin plainly enough to permit a direct removal of the cause, which, in other ("symptomatic") diseases, is often aggravated by the suppression of its external manifestations. In other words, Art is here competent to deal with the hostile "power behind phenomena," and Instinct resigns its mission to Reason.

It is still a mooted question if tuberculosis can be included among the "germ-diseases" of this class; but attention has been called to the circumstance that a certain stage of pulmonary consumption stimulates the sexual instinct to a degree which can hardly be supposed to benefit the exhausted state of the organism. The study of that indubitable fact offers a curious problem, but also a solution which considerably modifies the apparent paradox. The truth seems to be, that the tendency alluded to manifests itself only in a far advanced and practically hopeless stage of the disease, when Nature sacrifices the interests of the individual to those of the species. Moths, impaled in the collector's show-case, often pay an interest on the debt of Nature by a deposit of numerous eggs. Many plants ripen their fruit just before the end of the season. At the brink of Styx doomed men are apt to renounce individual cares and become eloquent for the benefit of posterity. It is Nature's law of reversion. It is also true that far-gone consumptives are very apt to indulge in exuberant hopes, belied by an event which they can hardly have helped to postpone.

But it is equally certain that, in a far larger number of diseases, instinct is the safest guide to recovery. The overloaded stomach rejects food; the exhausted system at last accepts no compensation but sleep. Wounded animals crouch motionless in their hiding-places; instinct informs them that rest increases the chances of recovery. The unrest of asthma-patients intimates the surest remedy—change of air and outdoor exercise. Fever-patients pant for refrigeration. Dyspepsia can be avoided by heeding the premonitory symptoms—the want of appetite that accompanies the first stage of chronic indigestion. In the incipient stages of scurvy, and many enteric disorders, the organism demands a change of diet as urgently as the perspiring skin clamors for a change of temperature. But when has that instinct ever clamored for drugs? If suppuration fails to dislodge a thorn, the skin of the inflamed parts becomes tenuous, and at last prurient, and not only tolerates but invites excision. We see, then, that instinct can adapt itself to abnormal circumstances, and the question recurs: In what state of distress does our stomach cease to protest against the compounds of the drug-monger? Or, shall we believe that our protective instincts, at the most critical moments, become false to their mission, and urgently warn us against the means of salvation? Yet, against ninety-nine of a hundred remedial drugs they protest with a persistence which can be overcome only by such juggles as lozenges and sugar-coated pills. That protest is a cliff which will ultimately wreck all the arguments of the castor-oil school. Home-sickness, if curable only by a counter-poison, inspires its victims to seek relief in friendship (attachment transferred to less inaccessible objects), and sometimes in religious fervor—yearning for a home which even an impecunious traveler may hope to reach. Pliny marvels "how greatly disappointed love inspires to deeds heroic"; yet heroism, in the ancient active sense, self-devotion to hard work and rough-and-tumble campaigns, is, in truth, the best cure for the ailments of sentimental sorrow. The mountain-mania of worn-out brain-workers, their passionate longing for the occupations of their nature-abiding ancestors—hunting, camping, and horticulture—are inspired by the instinctive desire to re-establish the structure of their organism on the basis of its original foundations, and recover, as an uprooted tree might revive in the mold of its native soil.

The purpose of such intuitions has rarely been fully recognized, and there is no doubt that the most useful contribution to the medical literature of this century would be a popular treatise on the Revelations of Instinct. The didactic significance of those revelations may even be destined to become the basis of a special science. That science would help the votaries of reform to atone for the grievous heresies of the past. It would make the healing art an ally of Nature: it would preserve us from manifold social and educational errors, by guiding progress along the lines of natural ordination. A science of instinct would be the commentary of a gospel which, in the language of man, has almost ceased to be its own interpreter.